Thermal cut-out



Dec. 3, 1929. s. w. oKEEFr-'E 1,737,674

THERMAL CUT OUT Filed Jan. 30. 1926 UMA/Mk.

Patented Dec. 3, 1929 UNITED STATES PATENT 'OFFICE GEORGE W. OKEEFFE, 0FDOECHESTER, MASSACHUSETTS, ASSIGNOR TO CONDIT ELEC- TRICAL MANUFACTURINGCORPORATION, 0F SOUTH BOSTON, MASSACHUSETTS, A

CORPORATION OF MASSACHUSETTS THERMAL CU T-OUT Applrifaition med Januaryao, 1926. serial No. 85,003.

This invention relates to protective devices, as thermal cut-outs, `forelectric circuits and is intended as an improvement on the inventiondisclosed in my/co-pending application Serial No. 755,347, filedDecember 11, 1924.

The thermal cut-out set forth in my above application includes a casingcontaining two separable current-carrying members united by a materialadapted readily to melt by the heat ofthe current traversing thecut-out, with means to separate the current-carrying members rapidlywhen the uniting material melts, whereby to interrupt the circuit.

The present invention has for an object the provision of means to entrapthe gases and metal vapors and particles formed by :the arc, duringcircuit interruption, and to prevent the metal vapors from condensingupon the wall of the enclosing casing and forming a conducting metalfilm between the circuit terminals.

A further object is to provide a singleuseenclosing casing whichsurrounds the current-carrying members and which is adapted to enclosethe circuit-interrupting arc and receive and retain themetal vapors-andparticles, which container is adapted to be thrown away after acircuit-interrupting are has taken place within it.

A further object is to provide means disposed adjacent the fusible massto cool and condensethe condensible metal vapors formed upon circuitinterruption.

A yet. further object is generally to improve the construction offusible cut-outs for electric circuits. k

Fig. 1 is a side elevation of a thermal cutout embodying my invention.

Fig. 2 is an enlarged sectional elevation taken through the verticalaxis of Fig. 1.

Fig. 3 is a perspective view, partly in section, of the fusible linkembodying the invention.

Fig. 4 is a plan view of the cut-out of Fig. 2 with the cover removedand with the fusible link in current-carrying position.

Fig. 5 is a view similar to Fig. 4 but illustrating the disposition ofthe component parts of the fusible link after the device has/ operatedto interrupt the circuit through it.

As here shown, the thermal cut-out embodying the present inventionincludes a casing 10 of insulating material formed with a recess 12 inthe upper portion thereof, which recess is normally closed by aremovablecover 14. The casing is provided with an integral boss 16 which supportsa screwthreaded shell 17 which-is adapted to be screwed into asuitablesocket and make connection with one of the terminals of the circuit tobe protected by the cut-out. Said boss is also provided with a contactmember 18 at its lower end, which member is adapted to make contactwithin the socket -with another terminal of the circuit to be protected.A post 20 is disposed within said recess 12 and within arecess 22 insaid boss and is screwthreaded rotatably within said contact member 18and is adapted to rotate in its connection therewith. A spring 24encircles said post and has its ends connected respectively to said postandito said casing and is adapted to urge said post for rotation.Rotaryrmovement of said post is normally restrained by the fusible-linkhereinafter to be described; and the rotation of said post is limited bythe engagement of a laterallyextended link-holding arm 26 thereof withlan abutment 28 of said casing. Said screwthreaded shell 17 is providedwith a contact terminal 30 whichextends upwardly into the recess 12in aposition remote from said abutment `28 and is provided with a bindingscrew 32 by which mechanicaland electrical connection is made with oneend of'the fusible link. The link-holding arm 26 is provided with anupwardly-extended hook 34 over which the other end of the fusible linkis adapted to be received.

The fusible link comprises two separable current-carrying members 36 and38 herein shown as composed of wire and preferably wire having arelatively high electrical resistance and adapted to become heated bythe passage of current through them. The proximate ends of said membersare juxtaposed and united mechanically and electrically by a mass 40 ofsolder or some readily fusible metal which is adapted to fuse or meltwhen the link becomes sufficiently heated and thereby to permit thecurrent-carrying members to be separated and consequently tointerrupttlie circuit. Said members are provided with refiexed orhook-terminals 42 and 44, one of which hooks is adapted to be re` ceivedunder the binding screw 32 and the other of which is disposed over thehook 34 of the arm 2G carried by the post 20. The spring Q4 associatedwith said post iis arranged to exert a tension upon the two parts of thefusible link and to separate them rapidly when the fusible metal meltsand releases them, whereby rapidly to attenuate the circuit-interruptingarc and interrupt the circuit.

After thefusible link has been severed the parts thereof are adapted tobe thrown away and replaced by a new and similar'link.

The apparatus above described is essentially the same as is set forth inmy abovenamed application.

In the operation of the cut-out as above described it has been foundthat, under certain conditions, the metal particles and vapors. formedupon the drawing of the arc, condense and collect upon the wall of therecess l2 and tend to form a metal conducting iilm thereon which liesbetween the terminals of the cut-out. The presence of such a conductinglilm is undesirable as it reduces the open-circuit insulation value ofthe'device and also presents the possibility of the circuit-interruptingare passing to the film and thereby rendering the extinction of the arcdiflicult. In addition, upon heavy loads, so much metal may bevaporizedas to build up a substantial and undesirable fluid pressure within thecasing.

For these and other reasons it is an object of this invention to providemeans to catch and absorb the gases and metal particles and condense andretain the metal vapors formed upon circuit interruption and to keepthem roizi'ined at the instant of circuit interruption and to preventthe metal vapor from being condensed and the inetal particles fromcollecting on the inner Wall of the casing. The aforesaid meanscomprises essentially a cylindrical cover or tube 46 which is disposedloosely upon the fusible llink, to cover the fusible metal thereof. Thevtube preferably cncloses the straight portion of the link on bolli sidesof the fusible metal and is held in place by the reflexed ends of thelink, which ends may be reiexed-after the tube is in place. Said tube iscomposed of some suitable heatresisting and electrically insulatingmaterial, as asbestos. The tube preferably is somewhat porous. Vhen themass 40 of fusible metal melts under heat, the circuit-interrupting areis drawn within the insulating tube. The tube acts to confine the arcgases and metal vapors and particles in close proximity to thelink-members. The arc products pass into the pores of the tube and areprevented from circulating throughout the casing, a.l though the ends ofthe tube are open and the are gases may escape to some extent from theopen ends. The metal vapors and melted particles of metal are collectedand condensed upon the cool inner wall of the tube. Aftercircuit-interruption fthe tube will be found upon either one or theother of the separable components of the fusible link, one of thecomponents having been withdrawn through the open end of the tube, or onthe bottom of the recess, free from the separated components. After acircuit-interruption the tube with any internal deposit of metalparticles it may have received is adapted to be thrown away, together-with the separated link-components, and replaced by a new tube on a newlink. Used in this manner, the cut-out is always provided with a freshsurface upon which the metal particles can collect and the metal vaporcan condense so that the inner' wall of the link-v compartment ismaintained free from any material metal deposit. The formation of asubstantial gas pressure is retarded, also.

The tube above set forth has been found materially to increase thecircuit-interrupting ability of the cut-out.

I claim:

1. A fusible link for an electric cut-out comprising two separablecurrent-carrying members united by a mass of readily fusible material,and a porous tubular cover of electricallyv insulating andheat-resisting material enclosing said fusible mass and adjacentportions of said current-carrying members loosely and adapted to retainin the pores the metal particles of the fused material, saidcurrent-carrying members extended outwardly beyond the open ends of saidcover and terminated in reieiiedl ends provided with hooks, the ends ofsaid cover being terminated at and held from displacement on said link`by said reflexed ends.

2. An electric cut-out comprising an enclosing casing provided with anouter screwthreaded terminal shell, a shaft rotatablysupported withinsaid casing along the axis of the shell, said shaft having alaterallyextended arm terminated close to the wall of said casing, meansurging said shaft to revolve'said arm transversely of said casingaxis, afixed circuit terminal disposed within said casing", a link disposedwithin andv adjacent the wall of said casing and connecting said fixedterminal and the end of isaid arm and adapted normally to hold said armfrom movement, said link comprising two separable current carryingmembers having proximate ends united with a readily fusible material andhaving hooked outer ends engaging said fixed terminal and arm, and aporous tubular cover of electrical insulating and heat resistingmaterial enclosing loosely said fusiai ible material and the proximateends of said current carrying members, said link characterized by thefusing of the fusible material connecting its current carrying membersupon overload and releasing said current carrying members for separatingmovement under the action of said arm and shaft, and said porousinsulating tubular cover characterized by retaining within its pores themetal particles of said fusible material and holding the particlesagainst contact with the side walls of said enclosing casing.

3. A thermal cut-out for electric circuits of the screw plug typeincluding a tubular insulating casing having external screw threads atone end by which it is adapted to l be supported and an enlargedinternal recess at its other end, a rigid conducting member extendedaxially of said tube and spaced from the insulating side Walls thereof,relatively separable terminal members disposed Within said recess, afusible link disposed in said recess at one side of said axialconducting member and closely adjacent the side walls thereof andconnected with and normally restraining said terminal members frommovement, said link comprising two separable contactcarrying membersunited with a readily fusible material and a porous cover ofelectrically insulating and heat-resisting material loosely enclosingsaid fusible member and adjacent portions o said current-carryingmembers and characterized by holding in its pores metal particles ofsaid fusible material and preventing the formation of a conducting filmon the proximate side Wall of said casing.

In testimony whereof, I have signed my name to this specification.

GEORGE W. OKEEFFE,

